Phosphino-ferrocene ligands

ABSTRACT

An improved process for hydroformylating an ethylenically-unsaturated compound to form an aldehyde derivative thereof in the presence of rhodium hydridocarbonyl in complex combination with an organic ligand, characterized by employing as said organic ligand a compound having two phosphino moieties, one being of the formula: ##STR1## and the other being of the formula: ##STR2## wherein R 1 , R 2 , R 1  &#39;, and R 2  &#39; are organic radicals at least one of which contains an electronegative substituent moiety. The presence of the electronegative substituent in the ligand leads to an increased ratio of linear aldehyde to branched-chain aldehyde in the hydroformylation reaction product.

BACKGROUND OF THE INVENTION

Processes for preparing carbonyl compounds, e.g., aldehydes byhydroformylating an ethylenically-unsaturated precursor in the presenceof a catalyst comprising rhodium hydridocarbonyl in complex combinationwith an organic ligand are well-known in the art and are now coming tobe of increasing industrial importance. Typical of such processes is thehydroformylation of propylene to form butyraldehyde. These rhodium-basedprocesses are now favored over the older technology wherein cobaltcarbonyl is the major catalyst component for several reasons, includingthe fact that the rhodium systems can be used under relatively mildreaction conditions. Also, of very great importance, therhodium-catalyzed systems can be controlled so as to yield a product inwhich the normal isomer of the aldehyde predominates over thebranched-chain isomer to a greater extent than has normally beenobtainable heretofore with the older reaction systems. It is to beunderstood that for most industrial purposes the normal aldehyde isstrongly preferred over the branched-chain isomer as in, for example,those systems in which an aldehyde is initially formed, as byhydroformylation, and then oxidized to form the corresponding carboxylicacid which is then used as an intermediate in the production ofsynthetic lubricant base stocks. Considering heptaldehyde, for example,this compound is of very great importance as an intermediate in theproduction of heptanoic acid, certain esters of which are excellent basestocks for synthetic lubricant formulation, whereas the correspondingbranched-chain acid is much less useful for this purpose.

More recently it has been discovered, as disclosed in Belgian Pat. No.840906 (Oct. 20, 1976) and British Pat. No. 1,402,832, that bidentateligands are particularly useful, with Belgian Pat. No. 840906 inparticular disclosing that certain bidentate ligands which arederivatives of ferrocene are capable of yielding, under very moderatehydroformylation reaction conditions, an unusually high ratio of normalisomer to branched-chain isomer in the aldehyde product without thenecessity of employing a high ratio of ligand to rhodium in thecatalyst. More specifically, Belgian Pat. No. 840906 discloses that,with the ferrocene-based ligands, including specificallydiphosphino-substituted ferrocenes, there is little need for maintainingin the reaction zone more than about 1.5 moles of the ferrocenederivative per atom of rhodium (equivalent to a phosphorus:rhodium moleratio of 3.0:1). More recently yet it has been discovered, as set forthin U.S. Patent application Ser. No. 783,121 filed on Mar. 31, 1977 by J.D. Unruh and L. E. Wade, that there is another family of bidentatehydroformylation ligands which gives commercially attractive resultssimilar to those of the ferrocene-based ligands, these newer ligandscomprising cyclic compounds having in the ring two adjacentphosphinomethyl-substituted carbon atoms which are in trans relationshipto one another and between which the dihedral angle of the transpositions is from about 90° to about 180°.

In view of the foregoing it can be seen that bidentate ligands, andparticularly diphosphino ligands, have come to be recognized as anadvance over the relatively simple ligands, normally monodentate, whichuntil recently have been considered typical and entirely satisfactory.

The industry continues, however, to seek further improvement in theserhodium-complex hydroformylation catalyst systems for several reasonswhich include (a) the recognition that any measures for reducingreaction pressure and temperature without suffering a loss in reactionconversion rate and normal:isoaldehyde ratio in the product will greatlyreduce operating cost and (b) rhodium and the ligands both being costly,anything to improve catalyst efficacy and catalyst longevity will reduceboth operating costs and investment cost. It is also to be kept in mind,of course, that the supply of rhodium available throughout the world islimited, so that obtaining maximum productivity per unit amount ofrhodium-based catalyst is in itself a matter of unusual importance.

It is, accordingly, an object of the present invention to provide animproved hydroformylation process employing catalysts comprising rhodiumhydridocarbonyl in complex combination with bidentate organic ligands,in particular diphosphino ligands. It is a further object to provide newligands for use in such rhodium-catalyzed hydroformylation processes,the use of which facilitates operation at lower catalyst concentrationsthan are required with prior-art ligands. It is a further object toprovide a method of general applicability for improving the efficacy ofa given ligand by incorporating into its molecule certain substituentmoieties which it has now been found have the effect of improving itsefficacy in hydroformylation reaction systems.

Other objects will be apparent from the following detailedspecification.

SUMMARY OF THE INVENTION

In accordance with the present invention, an ethylenically-unsaturatedcompound, e.g., an alkane, is hydorformylated to form an aledhydederivative thereof by reaction with a carbon monoxide-hydrogen synthesisgas in the presence of a liquid reaction medium which contains, as thehydroformylation catalyst, rhodium hydridocarbonyl in complexcombination with an additional organic ligand which is a compound havingtwo phosphino moieties, one being of the formula: ##STR3## and the otherbeing of the formula: ##STR4## wherein R₁, R₂, R₁ ', and R₂ ' areorganic radicals at least one of which contains an electronegativesubstituent moiety. It is strongly preferred that there be maintained inthe liquid reaction medium contained in the hydroformylation reactionsolvent at least about 1.5 moles of the ligand per atom of rhodium. Thatis, the ratio of phosphorus atoms to rhodium atoms in the catalyticcomplex should be at least about 3.0:1.0.

It will be understood that carbon monoxide and hydrogen are themselvesligands in the present catalyst systems, but the term "ligand" or"additional organic ligand" will be used hereinbelow to designate theligands which are employed in addition to carbon monoxide and hydrogento make up the improved catalyst systems to which the present inventionis directed.

The heart of the invention lies in the use of the electronegativemoiety-substituted "R" groups in the ligand, with maintenance of thephosphorus:rhodium ratio of at least 3:1 also being very important inoperating the process at maximum effectiveness. By using the presentimproved ligands in the presently-recommended ratio of ligand torhodium, the hydroformylation reaction yields a product which containsnormal and branched-chain aldehyde derivatives of the olefinic feedstockin which the ratio of normal to branched-chain aldehyde is surprisinglyhigher than would be obtained, under otherwise-identical reactionconditions of pressure, catalyst concentration, etc. when using as thecatalyst any of the prior-art catalysts even including the improvedbidentate ligands as described in, for example, Belgian Pat. No. 840906and British Pat. No. 1,402,832 previously discussed hereinabove.

It will be recognized that employment of the present improved catalystcomplexes does not require a knowledge of the exact manner in which therhodium is incorporated into the complete catalytically active complex.Broadly, it is known that the rhodium is in complex combination withligands comprising carbon monoxide and an additional organic ligand.More specifically the catalytically-active complex is considered to berhodium hydridocarbonyl in complex combination with an additional ligand(i.e., the improved ligands which are central to the present invention),but the present invention does not reside in any particular theory as tohow the rhodium complex is structured.

Aside from the employment of the present improved catalyst system, thereaction conditions which are used in the present process are those ofprior art as already generally understood, although it is not necessaryto employ catalyst concentrations as high as normally used in the priorart.

DETAILED DESCRIPTION OF THE INVENTION

The parent ligands, by which is meant the ligands the performance ofwhich is improved by incorporating into them the electronegativesubstituents of the present invention, include broadly all of thealready-known hydroformylation ligands which have at least two phosphinogroups as represented broadly by the formula: ##STR5## wherein R₁, R₂,R₁ ', and R₂ ' are organic, normally hydrocarbyl, groups and wherein Lis an organic moiety which may be substituted and which may be an organometallic compound as exemplified by ferrocene. More than two of thephosphino groups can be present (i.e., the ligand can be tridentate ortetradentate, for example) although as a practical matter there will beonly two phosphino moieties. To recapitulate, any known polyphosphinoligand will be improved in its efficacy by the incorporation of thepresent electronegative substituent groups, but diphosphino ligands areof particular industrial importance for the present purposes. Likewise,arsenic or antimony analogs of the phosphino-based ligands can also beemployed, although here again the phosphino ligands are of particularindustrial importance so that the present improvements are directedprimarily to them. Particularly useful parent ligands include, however,compounds in which L is either (a) ferrocene (to which thedihydrocarbylphosphino substituents are to be attached in the 1 and 1'positions) and (b) cyclic compounds which have in the ring two adjacentcarbon atoms each of which is attached to a methylene group (one of thetwo phosphino moieties then being attached to each of these methylenegroups). The latter category is particularly efficacious inhydroformylation processes when said two adjacent ring carbon atomshave, between their trans positions (to which said methylene groups areattached), minimum and maximum attainable dihedral angles which are,respectively, not less than about 90° and not more than 180°. It is tobe understood, however, as explained above, that L can be any organicmoiety, substituted or unsubstituted, the diphosphino derivatives ofwhich are known in the existing art to be useable as ligands inrhodium-catalyzed hydroformylation processes.

R₁, R₂, R₁ ', and R₂ ' can be alike or different, although as apractical matter they will ordinarily be alike since the synthesis ofligands in which these groups are different from one another iscomparatively difficult and the use of mixed phosphino substituentsprovides no additional advantage. Normally R₁, R₂, R₁ ' and R₂ ' arehydrocarbyl groups, perferably of from 1 to about 20, especially from 1to about 12 carbon atoms. They may be alkyl, aryl, cycloalkyl, aralkylor alkaryl, but phenyl groups are specifically useful and the precursorcompounds required for synthesizing the bis(diphenylphosphino) ligandsare readily available. Alternatively, R₁, R₂, R₁ ', and R₂ ' can besimple alkyl groups, especially of from about 1 to about 12 carbonatoms, precursor compounds for synthesizing phosphino moietiescontaining such lower alkyl groups being also available.

The electro-withdrawing moieties which are to be attached to thehydrocarbyl groups attached to the phosphorus atoms in the ligands are,broadly, all those moieties which are characterized by having a positiveHammett's sigma value as explained in Gilliom, R. D., Introduction toPhysical Organic Chemistry, Addison-Wesley, 1970, Chapter 9, pp.144-171. The higher the sigma value, the more efficacious thesubstituent moiety will be when employed in the present improvedprocess. The substituent should be attached to the hydrocarbyl group ata position such that it (the substituent moiety) will be separated fromthe phosphino phosphorus atom by not more than about six carbon atoms.When the hydrocarbyl radical is aryl, as exemplified by the phenylradical which is particularly suitable for the present purposes, thesubstituent moiety should be in the meta or the para position except,however, that, when the substituted hydrocarbyl radical is phenyl andthe substituent moiety is an alkoxy or hydroxyl group, then thesubstituent should be attached only at the meta position. (This isconsistent with the requirement set forth above that the Hammett sigmavalue be positive in all cases, since alkoxy and hydroxyl moieties inthe para position actually have a negative Hammett sigma value.)Acetylamino and phenyl groups are also negative in the para position,but as a practical matter these substituents are not likely to beencountered.

While it is to be understood that, as already explained, any substituentmoiety having a positive Hammett sigma value can be used, the followingsubstituent moieties are specifically illustrative: meta-fluoro;para-fluoro; para-trifluoromethyl; meta-trifluoromethyl;di-meta-trifluoromethyl; para-chloro; meta-chloro; para-bromo;meta-bromo; para-nitro (but only with exercise of caution in preparingand storing); para-cyano; and meta-methoxy (but not para-methoxy, asexplained above), ethoxycarbonyl, acetoxy, acetyl, acetylthio,methylsulfonyl; methylsulfanyl, sulfamoyl, and carboxy.

The benefits of inserting the above-described substituent moieties intothe hydrocarbyl (or, more broadly, organic) groups which are attached tothe phosphino phosphorus atoms to some extent when even one of the fourR groups is so substituted. The beneficial effect is additive, however(although not necessarily linear), so that it is preferred that all fourR groups have the electronegative substituents. Commonly, R₁, R₂, R₁ ',and R₂ ' will all be identical and each of these groups will also havethe same electronegative substituents attached to it. This is notessential, however, the use of mixed R groups having also mixedelectronegative substituents not being excluded.

When the hydrocarbyl group attached to the phosphorus atoms is alkylinstead of phenyl or other aromatic moiety, the same halo, haloalkyl,nitro, cyano, alkoxy, etc. electronegative substituents listed above canalso be employed although, of course, the terms "meta" and "para" wouldnot apply. In such cases, as previously explained, the electronegativesubstituent should be at such a position on the hydrocarbyl moiety thatit is separated from the phosphino phosphorus atom by not more thanabout 6 carbon atoms, preferably 1 to 4 carbon atoms.

While many alternatives and/or modifications will suggest themselves tothose skilled in the art, the preparation of theelectronegatively-substituted diphsophino ferrocene ligands for use inthe present improved process may be outlined as follows:

One begins with the Grignard reagent corresponding to theelectronegative-substituted moiety it is desired to incorporate into thesubstituted ligand which is ultimately to be synthesized. That is, forexample, when it is desired that the electronegative-substituted "R" inthe final ligand product is to be 4-trifluoromethylphenyl, one beginswith the Grignard reagent which is made from4-trifluoromethylbromobenzene. The Grignard reagent is then reacted with(CH₃ CH₂)₂ NPCl₂ (diethylaminodichlorophosphine) to form ##STR6## whichis then treated with anhydrous HCl to formbis(4-trifluoromethylphenyl)phosphinous chloride. The synthesis up tothis point is discussed in greater detail by K. S. Yudina, T. Y. Medved,M. I. Kabachnik, Izv. Akad Nauk, SSSR, Ser. Khim, 1954-58 (1966). Chem.Abstr., 66, 7609u (1967), and K. Issleib and W. Seidel, Chem. Ber. 92,2681-94 (1959).

An adduct of tetramethylethylenediamine and n-butyl lithium is thenformed in a suitable inert liquid, e.g., n-hexane, after which theadduct in the inert liquid is then slowly added to a solution offerrocene in, preferably, the same inert liquid, i.e., n-hexane.Following this, the bis(4-trifluoromethylphenyl)-phosphinous chloride isthen slowly admixed into the mixture of ferrocene and adduct thepreparation of which has just been described, to form the desiredelectronegatively-substituted ligand, which is a yellow-brown solid. Asmall amount of water is added to destroy any excess butyl lithium orchlorophosphine which may be present, and the solid adduct is thenfiltered out and washed with water and with liquid hexene. It is thendried, advantageously in a current of air at about ambient temperatureand/or in a vacuum chamber. This portion of the synthesis is analogousto the snythesis described by Bishop et al. in Bishop, J. J., et al., J.Organometal Chem, 27, 241 (1971).

To prepare the electronegatively-substituted ligands discussed hereinother than those based on ferrocene, one also begins with the Grignardreagent as discussed hereinabove and follows the same procedures downthrough and including the separation of the, for example,bis(4-trifluoromethylphenyl)phosphinous chloride. After this, however,the next step with this latter group of ligands is to react thebis(4-trifluoromethylphenyl)phosphinous chloride with metallic sodium ina dry mixture of dioxane and tetrahydrofuran to form the correspondingsodium phosphide. This is discussed more fully in Houben-Weyl "MethodenDer Organische Chemie", Volume 12/1, pp. 23-24. The phosphide is thenreacted with the ditosylate corresponding to the desired ligand bymethods which are described more fully in British Pat. No. 1452196(Rhone-Poulenc) and the more detailed literature sources which areidentified in that patent. British 1452196 presents a particularlyuseful discussion of the synthesis of ligands having two phosphinomoieties attached to cyclic structures, with the exception that it doesnot disclose the present improvement which lies in the incorporation ofthe electronegatively-substituted moiety into the diphosphino ligands.

Incorporating the ligand into the complete catalytic complex comprisingthe ligand and rhodium hydridocarbonyl can be carried out by methodsalready known to the art as exemplified, for example, by the disclosureof Belgian Pat. No. 840906 issued Oct. 20, 1976. Advantageously, forexample, a rhodium compound containing carbonyl moiety in themolecule--as exemplified by rhodium carbonyl itself--is simply mixedwith the ligand in a suitable inert liquid, which conveniently can bethe solvent which is to be used in the subsequent hydroformylationreaction itself (e.g., toluene or a liquid alkane or any of the manyknown hydroformylation reaction solvents including liquids comprisingpredominantly the hydrocarbon reactants and/or the hydroformylationreaction products themselves, which are usable as hydroformylationliquid reaction media even though they are not, strictly speaking,chemically inert). The resulting mixture of ligand and rhodium carbonylcan then simply be injected directly into the hydroformylation reactionzone, where, in the presence of hydrogen:carbon monoxide synthesis gasand under the conditions of pressure and temperature normally obtainedin hydroformylation reaction systems, the formation of the desiredcatalytic complex is completed.

Another useful rhodium source in forming the catalytic complex is thecomplex hydrocarbonyltris(triphenylphosphine)rhodium(I) orHRh(CO)(Pφ₃)₃. This is itself, of course, a complex of rhodiumhydridocarbonyl with a ligand (triphenylphosphine). To be industriallyattractive in hydroformylation reactions, however, it must be used witha substantial excess of the triphenylphosphine (i.e., substantially morethan a 3:1 ratio of triphenylphosphine to rhodium) by simply using thiscomplex as the rhodium source, however, in an improved complex whereinthe present improved ligand is also added, one obtains a greatlyimproved catalyst in which the triphenylphosphine moiety is only adiluent which contributes little if anything to the efficacy of themixture. Other sources of rhodium will also suggest themselves to oneskilled in the art and are discussed further hereinbelow.

As just explained, the complex is formed by introducing the ligand andthe rhodium source, along with a chloride scavenger if one is calledfor, into the hydroformylation reaction zone wherein, under theconditions obtaining therein, the catalytically active complex is formedin the presence of the synthesis gas. Enough ligand should be employedthat the resulting mixture of ligand and rhodium contains at least about3.0 phosphino moieties per atom of rhodium. A lower phosphorus:rhodiumratio results in reduced catalytic effectiveness, but these ligands arequite effective at phosphorus:rhodium ratios as low as 3.0:1. That is,there is a very definite increase in catalytic effectiveness of each ofthese ligands as the phosphorus:rhodium ratio is increased up to 3.0:1;the effect of further increases in the ratio is less pronounced. It is,of course, always desirable to maintain a phosphorus:rhodium ratio atleast slightly above 3:1 in order to be sure that the ratio does notinadvertently fall below this desired level as a result of, for example,metering errors that might occur in the course of adding rhodium andligand to a reactor especially at low flow rates.

As is already well understood in the existing art, the hydroformylationof an olefinic feedstock, e.g., an alkene, by processes of the presenttype is effected by introducing into a reaction zone contained in areaction vessel of coventional type the olefin to be hydroformylated (ineither gas or liquid form) along with a gaseous mixture of hydrogen andcarbon monoxide. The reaction vessel contains a liquid reaction mediumin accordance with the well-known technology of hydroformylationchemistry as further discussed hereinbelow, and the catalytic complex isdissolved or suspended in this liquid reaction medium. Tolueneexemplifies the usual inert solvents or reaction media used in thesesystems, but many other liquids can be employed, such as benzene,xylene, diphenyl ether, alkanes, aldehydes and esters, the aldehydes andesters often conveniently comprising products and/or byproducts of thehydroformylation reaction itself. Selection of the solvent is outsidethe scope of the present invention, which is drawn more particularly toimproving the catalysts for these reaction systems rather than to othermodifications of the system itself. In the reaction zone the catalyticcomplex serves to catlyze the hydroformylation of the olefin with thehydrogen and the carbon monoxide to form a mixture of aldehydescontaining one more carbon atom than the olefin reactant. Typically, itis desired to employ a terminally-unsaturated olefin, and it is normallypreferred that the terminal carbon atom be the site of attachment of thecarbonyl group which is introduced by the hydroformylation reaction. Thenature of the catalyst employed affects this matter of whether a normalaldehyde is produced (i.e., whether the terminal carbon atom of theolefin is the site of hydrocarbonylation as compared with the secondcarbon atom in the chain), and the present improved ligands impart verydesirable properties to the hydroformylation catalyst in this regard.That is, they produce a high proportion of aldehyde product in which theterminal carbon atom has been carbonylated.

The olefinically-unsaturated feedstock which is to be hydroformyulatedby the present improved process can be any of the many types of olefinalready known in the art to be suitable for rhodium-catalyzedhydroformylations, especially olefinic compounds having in the moleculeup to about 25 carbon atoms. Although mono-unsaturated compounds arenormally employed and of particular practical importance, di- andtri-ethylenically unsaturated olefins can also be used, the product ineach case being, if complete hydroformylation is carried out, aderivative having up to one additional carbon atom for each ethylenedouble bond in the parent compound. Olefinic compounds havingsubstituted groups, e.g., ethyenically-unsaturated alcohols, aldehydes,ketones, esters, carboxylic acids, acetals, ketals, nitriles, amines,etc. can be easily hydroformylated as well as the simple mono-alkeneswhich are particularly useful and of particular commercial importance.Broadly, ethylenically-unsaturated compounds which are free of atomsother than carbon, hydrogen, oxygen, and nitrogen are readilyhydroformylated, and more particularly compounds consisting solely ofoxygen, hydrogen, and carbon. Some specific classes of substitutedolefins to which the hydroformylation process is applicable are:unsaturated aldehydes such as acrolein and crotonaldehyde; alkanoicacids such as acrylic acid; and unsaturated acetals, such as acroleinacetal. More commonly, suitable hydroformylation feedstocks include thesimple alkenes such as ethylene, propylene, the butylenes, etc.;alkadienes such as butadiene and 1,5 -hexadiene; and the aryl, alkaryl,and aralkyl derivatives of the foregoing. Lower mono-alkenes of 2 toabout 12 carbon atoms are especially useful. Hydroformylation does notnormally take place within the benzene ring of olefins having arylsubstitution, of course, but rather in the ethylenicallyunsaturatedportion of the molecule.

Process operating parameters to be employed in practicing the presentprocess will vary depend upon the nature of the end product desired,since, as already known in the art, variation of operating conditionscan result in some variation in the ratio of aldehydes to alcoholsproduced in the process (some alcohol may be formed in small amountsalong with the aldehyde which is normally the desired product) as wellas the ratio of the normal to the branched-chain aldehyde derivative ofthe parent feedstock. The operating parameters contemplated by thepresent process are broadly the same as those conventionally employed inhydroformylation processes using rhodium complexes as already known inthe art. For the sake of conveninece, these parameters will be generallyset forth hereinbelow; it being understood, however, that the processparameters are not critical to achieving the improved results of thepresent invention as compared with processes using the prior-art ligandsand do not, per se, form a part of it. That is, the present improvementlies in the use of the present improved ligands and not in theconcomitant employment of any change from existing rhodiumhydroformylation technology as already known to the art. To repeat thepoint, using the present improved catalyst system does not necessitateany departure from rhodium-catalyzed hydroformylations as already known,except for changing the ligand.

In general, the hydroformylation process is conducted under a totalreaction pressure of hydrogen and carbon monoxide combined of oneatmosphere or even less, up to a combined pressure of about 700atmospheres abolute. Higher pressures can be employed but are normallynot required. For economic reasons, however, pressures significantlygreater than about 400 atmospheres absolute will not normally beemployed.

The reaction is normally conducted at a temperature of from about 50° toabout 200° C., with a temperature within the range of about 75° C. toabout 150° C. being most commonly employed.

The ratio of partial pressures of hydrogen to carbon monoxide in thereaction vessel may be from about 10:1 to about 1:10 in accordance withthe prior art, although it has been discovered that when using thepresent ligands this range may even be extended to about 50:1 to 1:50.Normally, however, the range of hydrogen partial pressure to that ofcarbon monoxide will be from about 6:1 to about 1:1, with ahydrogen:carbon monoxide ratio of about 1:1 usually being employed.

As is also known from the prior art, a liquid reaction medium isemployed. Frequently this can comprise the ethylenically-unsaturatedfeedstock itself when it is liquid under the conditions existing in thereaction zone. A separately-added solvent can be employed if desired,however, particularly when the feedstock is of high volatility such thatmaintaining a liquid phase would require maintenance of excessivepressure under the reaction temperature which is to be employed. Whenthe solvent is to be liquid other than the olefinic reactant or aproduct of the hydroformylation process (high-boiling reactionby-products are known to be useful for the purpose), it is preferredthat it be one which is inert toward the catalyst and reactants underconditions obtaining within the reaction zone. Suitable reactionsolvents include: benzene, toluene, diphenyl ether alone or mixed withbiphenyl, esters, polypropylene oxides, ketones, aldehydes, ethyleneglycol, alkanes, alcohols, and lactones.

Whatever may be the composition of the liquid reaction medium (i.e.,whether it comprises predominantly a separate reaction solvent or areaction feedstock or reaction product or by-product), the catalystcomplex should be maintained in it at a concentration of about 0.1 to 50millimoles/l calculated as rhodium. More preferably, about 0.5 to 20.0millimoles/l of rhodium is recommended. While the catalyst can be formedex-situ, it is conveniently prepared in-situ in the liquid reactionmedium by introducing the ligand along with a suitable rhodium sourceand then allowing complexation to occur under the temperature to beemployed in the hydroformylation reaction and in the presence of thehydrogen:carbon monoxide gas mixture which is to be used in thehydroformylation process. A suitable rhodium source is HRh(CO)Pφ₃)₃.Other rhodium sources which can be used include:rhodium on carbon, Rh₂O₃, Rh(NO₃)₃, Rh₂ (SO₄)₃, RhCl₃ ·3H₂ O, RhClCO(Pφ₃)₂, [Rh(CO)₂ Cl]₂[Rh(2,5-cyclooctadiene)Cl]₂, RhBr₃, and RhI₃. If a halogen-containingrhodium source is to be employed, it is desirable to include with it asufficient quantity of an alkaline reactant (e.g., sodium hydroxide) toscavenge the halide moiety out of the system as the complex is formed.

The following examples are given to further illustrate the practice ofthe invention. It will be understood that many variations can be madetherefrom in accordance with the explanations given hereinabove.

EXAMPLE 1 (Run 24861-36)

As an initial step in preparing 1,1'-bis[bis(4-trifluoromethylphenyl)phosphino]ferrocene (hereinafter PTFL), 1,1'-dilithio ferrocene wasprepared as follows:

A reactor was employed which comprised a 1-liter 3-neck flask equippedwith a mechanical stirrer, reflex condenser, dropping funnel, and aconnection for introducing nitrogen. Into the flask there was firstintroduced nitrogen. Into the flask there was first introduced 0.02339mole of ferrocene and 300 ml of hexane. Next, 0.047 mole of n-butyllithium (as a 2.4 M solution in hexane) was mixed in the dropping funnelwith 0.047 mole of tetramethylethylenediamine, and the resulting adductdissolved in hexane was added dropwise to the flask over a period ofabout 15 minutes. The reaction mixture was allowed to stand, withstirring, overnight under a nitrogen atmosphere.

EXAMPLE 2 (Run 24861-3,4)

In a two-liter three-neck flask equipped with a condenser, droppingfunnel, stirrer, and nitrogen purge connection as in Example 1 abovethere were placed 1.056 moles of pyridine and 0.176 mole ofdiethylaminodichlorophosphine in about 400 ml of anhydrous diethylether. The contents of the flask were then cooled to between -5° and-10° using an ice-water-salt bath. Next, over a period of 45 minutesthere was added 0.44 mole of para-trifluoromethylphenylmagnesiumbromide. The contents of the flask were then allowed to warm up to roomtemperature and the resulting light brown-colored slurry was stirredovernight. The slurry was then filtered to recover the desired product,which has a reddish brown filtrate the solids on the filter were alsowashed three times with diethyl ether, the washings being combined withthe filtrate.

EXAMPLE 3 (Run 24861-4)

The reddish brown filtrate from the preceding example was placed in aone-liter three-neck round-bottom flask equipped with a condenser,stirrer, and sparger. Gaseous HCl was then added through the sparger ata very slow rate. Immediately a white precipitate started to form whilethe color of the solution changed from reddish brown to orange. Withcontinuing addition of HCl, a thick yellow slurry formed in the flask.As further quantities of HCl gas were added, the solids began todisappear, finally leaving in the flask a two-phase liquid which wasyellow in color. Upon the evaporation of some of the liquid (diethylether) a white solid began to separate. This was filtered out and washedwith dry anhydrous ether. The filtrate and washings were combined andthe ether was separated from the resulting mixture by evaporation. Afterthis the remaining liquid residue was subjected to vacuum distillation,the resulting distillate (collected at 110° C. and 0.4 mmHgA) wasexamined by nuclear magnetic resonance methods and confirmed to be purebis(para-trifluoromethylphenyl)phosphinous chloride. The yield was 39.1grams.

EXAMPLE 4 (Run 24861-5)

The following describes the preparation of1,1'-bis[di(para-trifluoromethylphenyl)phosphino]ferrocene usingintermediates as prepared in the preceding examples.

In a 500 ml three-neck round-bottom flask equipped with a condenser,dropping funnel, and mechanical stirrer and having means for maintaininga nitrogen atmosphere therein, there were dissolved 29.8 millimoles ofpurified sublimed ferrocene in 250 ml of n-hexane. In the droppingfunnel 60 millimoles of tetramethylethylenediamine were mixed with 60millimoles of n-butyl lithium (as a solution of approximately 2M inhexane) to form an adduct of these two compounds. The adduct was thenadded from the dropping funnel into the ferrocene solution in the flaskslowly, with stirring and while purging the flask with nitrogen. Theresulting mixture was then allowed to stir overnight at ambienttemperature and at atmospheric pressure.

After standing overnight, the lithiated ferrocene solution which had nowbeen formed in the reaction flask and which was of an orange color wasthen cooled to about -5° to -10° C. using a water-ice-sodium chloridebath. Next, 59.6 millimoles ofbis(para-trifluoromethylphenyl)phosphinous chloride was added dropwiseto the flask. After this addition was completed the resulting mixturewas allowed to warm up to room temperature while being continuouslystirred, forming in the flask a dark brown colored homogeneous solution.To this solution there was then added 30 ml of methanol to decompose anyunreacted n-butyl lithium, after which the contents of the flask wereextracted three times with 300 ml of water at each extraction.

The organic layer from the extraction was then placed in a 1000 ml flaskand all the liquid was evaporated therefrom. The resulting solids werethen washed twice with n-hexane, using about 200 ml each time. This wasfollowed with a diethyl ether wash. The resulting washed solids productwas then dried in a vacuum. The ether washings were also evaporated andthe resulting solids were likewise dried. The hexane washings wereevaporated and dried in the same way. The primary solids productobtained from evaporating the organic layer from the extraction amountedto 1.8 grams and had a melting point range of 153° to 156° C. By protonmagnetic resonance examination, this material was at least 95% pure1,1'-bis[di(para-trifluoromethylphenyl)phosphino]ferrocene. The solidsobtained from the evaporation of the ether washings amounted to 1.7grams and melted at 127° to 155° C., while the solids obtained byevaporation of the hexane washings amounted to 10.0 grams and melted at130 to 145° C. The 1.8 grams melting at 153°-156° C. were used as the"PTFL" liquid in those of the runs described below in which this was theligand employed.

In the examples which are to follow, use is made of certainabbreviations to designate the ligands which were employed in theseveral hydroformylation runs described therein. These are tabulatedbelow, the abbreviation being listed first, followed then by a briefchemical name and, finally, the complete chemical name. Of these thePCFL, the MFFL, and the PTFL are improved ligands within the ambit ofthe present invention:

Fl:ferrocene ligand:1,1'-bis(diphenylphosphino)ferrocene

Pmfl:p-methoxy ferrocene ligand:1,1'[di(4-methoxyphenyl)phosphino]ferrocene

Pcfl:p-chloro ferrocene ligand:1,1'-bis[di(4-chlorophenyl)phosphino]ferrocene

Mffl:m-fluoro ferrocene ligand:1,1'-bis[di(3-fluorophenyl)phosphino]ferrocene

Ptfl:p-trifluoromethyl ferroceneligand:1,1'-bis[di(4-trifluoromethylphenyl)phosphino] ferrocene

Dtfl:di-m-trifluoromethyl ferrocene ligand:

1,1'-bis(bis[3,5-bis(trifluoromethyl)phenyl]phosphino) ferrocene

Unless otherwise indicated, the operating procedure which was employedin each of the examples which are to follow hereinbelow was as follows.

A 300 ml stirred stainless steel autoclave was charged with toluene asinert reaction solvent, typically 60 ml, along with rhodium, normally asHRh(CO)(Pφ₃)₃ in an amount to obtain the desired molar concentration ofrhodium as indicated in the tables. Also charged to the reactor was thedesired amount of the indicated ligand, in an amount sufficient toobtain the indicated ligand concentration. In certain cases the ligandwas known to be impure, but this was compensated for by always addingsufficient ligand that the molar ratio of pure ligand to rhodium wouldbe in all cases at least 1.5:1. The autoclave was then closed andflushed several times with synthesis gas, which was a 1:1 mixture ofhydrogen and carbon monoxide. The autoclave was then pressured to theindicated 1:1 hydrogen:CO synthesis gas pressure after which itstemperature was adjusted to the indicated reaction temperature of about110° C. Next, 1-hexane, which had been preheated to the reactiontemperature, was pressured into the autoclave from a reservoir which waspressured by the 1:1 synthesis gas. Unless otherwise indicated, 20 ml ofthe 1-hexane was used. It is to be noted that hexane was used throughoutthese runs for the reason that it is comparatively easy to handle underlaboratory conditions. Other olefinic feedstocks such as propylene canbe used, as explained hereinabove.

Additional synthesis gas was then admitted into the autoclave from anexternal reservoir (which was maintained continuously at a pressurehigher than that of the autoclave) so as to attain and subsequentlymaintain, in the autoclave the desired indicated reaction pressure.

Upon attainment of the desired autoclave reaction pressure, the run wastaken as having been started, and thereafter the progress of thereaction was monitored by continuously observing the rate at which thepressure in the external synthesis gas reservoir declined as the gascontained was consumed in the reaction autoclave. When the rate ofreaction had dropped to an extremely low level, as indicated by a verylow rate of decline of the synthesis gas reservoir pressure, theautoclave was cooled to ambient temperature and its contents wereremoved and analyzed chromatographically.

EXAMPLE 5

The following are the results obtained when hydroformylating 1-hexene bythe procedure outlined immediately above, using a variety of ligands asshown. The run using PMFL ligand illustrates that this ligand, which hasa negative Hammett's sigma value, gives less satisfactory results thanobtained with the FL ligand which has a sigma value of 0.0. Theremaining three tabulated runs show increasingly beneficial results, asmeasured by the normal:iso ratio in the aldehyde products, as the sigmavalue of the substituent is increased from 0.227 to 0.540. The ligandswhich were employed in these runs were not all of high purity, butsufficient excess of ligand was used in each case that it was certainthat the ratio of contained pure ligand moiety to rhodium was at least1.5:1.

                                      TABLE I                                     __________________________________________________________________________    Rh CATALYZED HYDROFORMYLATION OF 1-HEXENE, 50 psig                            Run No..sup.(a)                                                                           24844-42                                                                            22959-46.sup.(c)                                                                    24844-26*                                                                           23054-35                                                                           24844-36                                                                           24844-49                              __________________________________________________________________________    Rh conc., mM                                                                              0.625 2.5   0.625 1.25 1.25 1.25                                  Ligand      PMFL  FL    PCFL  MFFL PTFL DTFL                                  Conc., mM.sup.(b)                                                                         3.75  5.0   3.75  3.41 3.75 3.75                                  Temp., ° C.                                                                        110 ± 0.5                                                                        110 ± 0.5                                                                        110 ± 1                                                                          109 ± 1                                                                         110 ± 1                                                                         110 ± 1                            Pres. of 1:1 H.sub.2 :CO, psig                                                             52 ± 2                                                                           50 ± 1                                                                           52 ± 2                                                                           51 ± 2                                                                          51 ± 1                                                                          50 ± 2                            n/iso ratio 5.37  6.19  8.64  10.1 13.7 11.6                                  % Ald, which is n                                                                         84.3  86.1  89.6  91.0 93.2 92.1                                  Conv., %    98.2  99.8  99.6  99.4 ˜100                                                                         99.6                                  K.sub.obs /mM Rh, min.sup.-1                                                              0.018 0.047 0.060 0.028                                                                              0.111                                                                              0.038                                 Eff. to prod., %                                                              Heptanal    81.6  84.3  81.2  81.9 79.8 81.6                                  2-Methylhexanal                                                                           15.2  13.7  9.4   8.1  5.8  15.2                                  2-Hexene    2.7   0.7   8.3   8.9  13.1 2.7                                   Hexane      0.5   1.3   1.1   1.1  1.3  0.5                                   σ Value of substituent.sup.(d)                                                      -0.268                                                                              0.0   0.227 0.337                                                                              0.540                                                                              0.430                                 __________________________________________________________________________     .sup.(a) Except for the "*" run, 60 cc of toluene and 20 cc of 1-hexene       were used. In the "*" run these amounts were halved.                          .sup.(b) Since some of the ligands were impure, enough ligand was used to     insure ligand/Rh ratios of at least 1.5:1 in all cases.                       .sup.(c) In this run Rh(CO)(FL)Cl was used as the source of Rh and 1/2 of     the FL.NaOH was added to the reaction mixture to remove Cl. All other run     used HRhCO(Pφ.sub.3).sub.3 as the Rh source.                              .sup.(d) Hammett's sigma value as previously explained.                  

The preceding Table I presents the results of hydroformylation reactionscarried out at a pressure of 50 psig. The following Table II presentsresults obtained with the same ligand but operating at 100 psig. It willbe noted here again that the PTFL ligand, which has the highest sigmavalue of the ligands tested, gave the most attractive results asmeasured by normal:iso ratio in the aldehyde product.

                                      TABLE II                                    __________________________________________________________________________    Rh CATALYZED HYDROFORMYLATION OF 1-HEXENE, 100 psig                           Run No..sup.(a)                                                                           24844-28                                                                            22959-43.sup.(c)                                                                    24844-4*                                                                            24885-31                                                                           24844-35                                                                           24917-1                               __________________________________________________________________________    Rh conc., mM                                                                              0.625 2.50  1.25  1.25 1.25 1.25                                  Ligand      PMFL  FL    PCFL  MFFL PTFL DTFL                                  Conc., mM.sup.(b)                                                                         3.75  5.0   7.50  2.50 3.75 3.75                                  Temp., ° C.                                                                        110 ± 1                                                                          110 ± 1                                                                          110 ± 0.5                                                                        110 ± 1                                                                         110 ± 1                                                                         110 ± 1                            Pres. of 1:1 H.sub.2 :CO, psig                                                            102 ± 3                                                                          101 ± 1                                                                          101 ± 2                                                                          100 ± 2                                                                         100 ± 1                                                                         100 ± 2                            n/iso ratio 4.77  5.59  6.65  8.15 12.4 11.9                                  % Aid, which is n                                                                         82.7  84.8  86.9  89.1 92.6 92.2                                  Conv., %    99.4  99.8  99.9  ˜100                                                                         99.9 99.2                                  K.sub.obs /mM Rh;min                                                                      0.028 0.027 0.042      0.091                                                                              0.030                                 Eff. to prod., %                                                              Heptanal    80.5  83.8  81.3  83.0 86.4 81.5                                  2-methylhexanal                                                                           16.8  15.0  12.2  10.2 7.0  6.8                                   2-Hexene    2.2   0.6   5.8   6.0  5.9  10.7                                  Hexane      0.5   0.6   0.7   0.8  0.7  0.9                                   σ Value of substituent.sup.(d)                                                      -0.268                                                                              0.0   0.227 0.337                                                                              0.540                                                                              0.430                                 __________________________________________________________________________     .sup.(a) Except for the "*" run, 60 cc of toluene and 20 cc of 1-hexene       were used. In the "*" run these amounts were halved.                          .sup.(b) Since some of the ligands were impure enough ligand was used to      insure ligand/Rh ratios of at least 1.5:1 in all cases.                       .sup.(c) In this run Rh(CO)(FL)Cl was used as the source of Rh and 1/2 of     the FL.NaOH was added to the reaction mixture to remove Cl. All other run     used HRhCO(Pφ.sub.3).sub.3 as the Rh source.                              .sup.(d) Hammett's sigma value as previously explained.                  

The synthesis gas used in the runs tabulated above was a 1:1 mixture ofhydrogen and carbon monoxide. This mixture was chosen (a) because it wasa convenient basis for comparison of the several ligands etc., and (b)because the net input of synthesis gas into an operatinghydroformylation system is normally about 50% hydrogen and 50% carbonmonoxide. As previously explained, however, other synthesis gascompositions can be employed if desired and, in a continuously operatinghydroformylation reaction system with recycles, the gas actuallycirculating through the reaction zone may have a higher ratio ofhydrogen to carbon monoxide, e.g., up to about 15:1 in many instances.The higher ratios are actually to be preferred in an industrialinstallation. For example, increasing the hydrogen:carbon monoxide ratiofrom 1:1 up to 4:1, by leaving the carbon monoxide partial pressureunchanged while increasing the hydrogen partial pressure to obtain thedesired ratio, increases the ratio of normal aldehyde to iso-aldehyde inthe hydroformylation product. This effect is demonstrated in Table IIIwhich is set forth hereinbelow, which indicated a levelling off of theeffect at about 3:1.

With regard to the variations in the synthesis gas pressure to bemaintained in the hydroformylation reaction zone, it has been observedthat the ratio of normal aldehyde to iso-aldehyde in the product tendsto decrease with increasing pressure when the partial pressure of 1:1synthesis gas is much above the range of about 50 to 100 psi, so thatthe partial pressure of 1:1 synthesis gas need not be much above about50 to 100 psi (equivalent to a carbon monoxide partial pressure of about25 to 50 psi). Increasing the hydrogen partial pressure, while leavingthat of the carbon monoxide unchanged, has beneficial results asexplained above. In converting hexene to heptanal (i.e., whenhydroformylating 1-hexene), the efficiency of conversion of the hexeneto the desired heptanal with a 1:1 synthesis gas is slightly greater at70 psi partial pressure of the 1:1 synthesis gas than at about 50 psi.At about 40 psi and below, the efficiency to heptanal begins to decline.Thus, a partial pressure of 1:1 synthesis gas of about 50 to 100 psi isnormally preferred. In connection with these comments regardingpressures, it should be noted that the several runs which are presentedherein express pressure in terms of psig, which is what was actuallymeasured. This includes, of course, the pressure exerted by liquids suchas the hexene, which amounts to about 1 atmosphere.

EXAMPLE 6

The following illustrates the effect of hydrogen:carbon monoxide ratioin runs which are otherwise carried out under the same conditions asemployed in Example 5.

                                      TABLE III                                   __________________________________________________________________________    Rh CATALYZED HYDROFORMYLATION OF 1-HEXENE                                     WITH PTFL LIGAND AT VARYING H.sub.2 :CO RATIO                                 Run No.   24844-36                                                                            24885-39                                                                            24885-40                                                                           14917-14                                                                           24885-41                                                                           14917-17                                                                           24885-42                                                                            24917-15                      __________________________________________________________________________    Rh amt., mmoles                                                                         0.10  0.05  0.05 0.05 0.05 0.05 0.05  0.05                          PTFL amt.,mmoles                                                                        0.30  0.15  0.15 0.15 0.15 0.15 0.15  0.15                          PTFL/Rh ratio                                                                           3.0   3.0   3.0  3.0  3.0  3.0  3.0   3.0                           Temp., ° C.                                                                      110.5 ± 1.5                                                                      110.5 ± 0.5                                                                      110 ± 1                                                                         110 ± 1                                                                         110 ± 1                                                                         110 ± 1                                                                         110.5 ± 1.5                                                                      110 ± 1                    Pres., psig                                                                              50 ± 2                                                                           75 ± 2                                                                          101 ± 2                                                                         101 ± 2                                                                         126 ± 2                                                                         125 ± 2                                                                         176 ± 2                                                                          175 ± 2                    H.sub.2 :CO ratio                                                                       1:1   2:1   3:1  3:1  4:1  4:1  6:1   6:1                           CO, psig  25    25    25   25   25   25   25    25                            n/iso ald. ratio                                                                        13.7  17.1  21.7 20.3 19.1 22.7 21.8  21.8                          % ald. that is n                                                                        93.2  94.5  95.6 95.3 95.0 95.8 95.6  95.6                          Conv, %   99.9  99.9  99.9 99.9 99.9 99.9 99.9  99.9                          K.sub.obs,min.sup.-1                                                                    0.138 0.124 0.149                                                                              0.154                                                                              0.143                                                                              0.143                                                                              0.169 0.151                         K.sub.obs /mM Rh                                                                        0.111 0.198 0.238                                                                              0.247                                                                              0.228                                                                              0.229                                                                              0.270 0.241                         Eff. to prod., %                                                              Heptanal  79.8  81.4  84.4 84.6 81.7 84.5 83.4  84.5                          2-Mehexanal                                                                             5.8   4.7   3.9  4.2  4.3  3.7  3.8   3.9                           2-Hexene  13.1  11.6  9.3  8.7  10.0 8.7  8.5   7.6                           Hexane    1.3   2.3   2.4  2.5  4.0  3.1  4.3   4.0                           __________________________________________________________________________

When, as in the foregoing examples, the hydroformylation reactionproduct is heptanal or other like aldehyde which is a liquid under thepressure and temperature conditions obtaining within the reaction zone,the product aldehyde is recovered from the liquid reaction medium bydistillation of the liquid reaction medium in a separate step or stepswhich are known to the art and which are outside the scope of thepresent invention. Also, it is feasible and desirable in these cases toconduct the hydroformylation reaction under conditions such that, asdemonstrated in the preceding examples, there is a high conversion ofthe olefinic feedstock so as to minimize processing complicationsinherent in separating a reaction product which contains a substantialfraction of unconverted feedstock. For example, when the feedstock is analkene having more than three carbon atoms, some migration of theterminal double bond is experienced such that a relatively inertinternally-unsaturated alkene builds in the reaction system whereby anyrecycled olefin would contain increasing proportions of this material.

However, when hydroformylating alkenes such as ethylene and propylenewhich are not liquid under the hydroformylation reaction conditions andwhich (specifically in the case of ethylene and propylene) do not havethe problem of internal migration of the double bond, the reaction iscarried out, as also known in the art, in a manner which, as regardsolefin conversion and the mode of aldehyde product recovery, differsfrom the techniques employed with higher olefinic feedstocks such ashexene. Specifically, the gaseous olefin feedstock is circulated, as bysparging, through the liquid reaction medium rather than being admixedthereinto as a liquid. A mixture of unreacted olefin synthesis gas, andaldehyde product is continuously withdrawn from the reaction zone in thevapor phase, and the aldehyde product is separated therefrom bycondensation. The unreacted gas mixture is then recycled back to thereaction zone, typically after withdrawing a slipstream therefrom forthe purpose of preventing buildup of inert contaminants. It will beunderstood, of course, that the recycling gas stream is continuouslymonitored and that carbon monoxide, hydrogen, and olefin arecontinuously injected into it so as to maintain the desired proportionsof these components in the gas being sparged into the liquid reactionmedium.

In hydroformylating either ethylene or propylene, it is recommended thatthe reaction zone be maintained at a temperature of about 80° to 120° C.and that the mixture of olefinic feedstock and synthesis gas beingsparged therethrough comprise about 10 to 40% olefin, 5 to 30% carbonmonoxide, and 40 to 70% hydrogen with the total pressure beingapproximately 5 to 30 atmospheres absolute. The liquid reaction mediumshould contain about 0.01 to 1.0% rhodium. The reaction medium can be,as previously explained, a separately-added inert liquid such asdiphenyl ether, xylene, toluene, or polypropylene oxide. Alternativelyit can be a mixture of high-boiling by-products of the hydroformylationreaction as already known in the art.

In hydroformylating 1-octene to produce nonanal, which, like the hepteneformed by hydroformylating 1-hexene, can be oxidized to form theindustrially-useful corresponding alkanoic acid, the recommendedprocessing parameters are the same as when hydroformylating 1-hexene.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
 1. 1,1'Bis[di(4-chlorophenyl)phosphino]ferrocene.
 2. 1,1'-Bis[di(3-fluorophenyl)phosphino]ferrocene.
 3. 1,1'-Bis[di(4-trifluoromethylphenyl)phosphino]ferrocene. 